Java Reference
In-Depth Information
try
{
int x = 1/0;
}
catch (ArithmeticException ae)
{
System.out.println("attempt to divide by zero");
}
Whenexecutionentersthetryblock,anattemptismadetodivideinteger1byinteger
0. The JVM responds by instantiating
ArithmeticException
and throwing this
exception.Itthendetectsthecatchblock,whichiscapableofhandlingthrown
Arith-
meticException
objects,andtransfersexecutiontothisblock,whichinvokes
Sys-
tem.out.println()
to output a suitable message—the exception is handled.
Because
ArithmeticException
isanexampleofanuncheckedexceptiontype,
and because unchecked exceptions represent coding mistakes that must be fixed, you
typicallydon'tcatchthem,asdemonstratedpreviously.Instead,youwouldfixtheprob-
lem that led to the thrown exception.
Tip
Youmightwanttonameyourcatchblockparametersusingtheabbreviatedstyle
shownintheprecedingsection.notonlydoesthisconventionresultinmoremeaningful
exception-oriented parameter names (
ae
implies that an
ArithmeticException
object has been thrown), it can help reduce compiler errors. For example, it is com-
monpracticetonameacatchblock'sparameter
e
,forconvenience.(Whytypealong
name?) However, the compiler will report an error when a previously declared local
variable or parameter also uses
e
as its name—multiple same-named local variables
and parameters cannot exist in the same scope.
Handling Multiple Exception Types
You can specify multiple catch blocks after a try block. For example,
Listing 3-25
'
s
convert()
methodspecifiesathrowsclauseindicatingthat
convert()
canthrow
InvalidMediaFormatException
, which is currently thrown, and
IOExcep-
tion
,whichwillbethrownwhen
convert()
isrefactored.Thisrefactoringwillres-
ultin
convert()
throwing
IOException
whenitcannotreadfromthesourcefile
orwritetothedestinationfile,andthrowing
FileNotFoundException
(asubclass
of
IOException
)whenitcannotopenthesourcefileorcreatethedestinationfile.All
these exceptions must be handled, as demonstrated in
Listing 3-26
.
